Aquatic Conservation: Marine and Freshwater Ecosystems

Reef manta rays (Mobula alfredi) are threatened by fishing and other anthropogenic threats. Which, when coupled with conservative life history traits, have made this species vulnerable to extinction. Spatiotemporal ecological knowledge, such as site fidelity and visitation patterns to key aggregation sites, are imperative for effective conservation management of M. alfredi. A novel method of environmental sensing, remote underwater photo systems (RUPs), was employed to understand drivers of M. alfredi habitat use and resighting patterns. RUPs were deployed at four cleaning sites around Laamu Atoll, Maldives. Between March 2021 and May 2023, 455,458 photos were analysed. Generalised linear models revealed increases in M. alfredi presence in response to high chlorophyll-a concentrations, low illumination moon states, the Southwest Monsoon, and in the morning, while human presence had no effect. Branchial spot patterns allowed for 81 M. alfredi individuals to be identified, from 629 sightings, representing 51.59% of Laamu Atolls previously identified population (n = 157). Cleaning stations are visited more intensively during periods of increased productivity of the Southwest Monsoon, likely in response to greater foraging opportunities near the study areas. Additionally, moon state, used as a proxy for tidal strength, was associated with increased visitation during new moon periods, suggesting that weaker tidal states may facilitate presence. These data support integrating RUPs with observational surveys to improve inferences about habitat use and our understanding of cleaning sites frequented by M. alfredi. This study aims to inform the implementation of Laamu Atolls first marine protected area management plan.

The white shark Carcharodon carcharias (Linnaeus, 1758) is one of the most iconic and threatened marine predators globally and is listed as critically endangered by the IUCN in the Mediterranean Sea, where populations are primarily affected by fishing pressure and the degradation of critical habitats. Available information on Mediterranean white sharks mostly relies on fishing interactions and opportunistic surface records, thereby limiting evaluations on the species ecology. Here, we report an exceptionally rare underwater encounter with this species, documented by divers involved in an expedition aimed at removing ghost fishing gear from a World War II shipwreck in the Strait of Sicily (SoS), central Mediterranean. Given the exceptional nature of this observation, we analysed the video footage in detail with the aim of providing morphological information and novel insights into the species ecology. The footage analysis also allowed close observations on behavioural aspects and on interspecific and parasitic associations, thus providing information that is rarely achievable through surface sightings or from captured individuals, which historically represent the majority of records for this species in the region. To contextualize this observation within the SoS--an area suggested to function as a nursery and reproductive ground for the species--we also provide an updated compilation of records reported in the scientific literature over the last decade, adding 18 new records to existing datasets. This study highlights the value of shipwrecks as observation sites for rare and elusive species, and underscores the importance of non-invasive, video-based approaches in advancing knowledge of a species whose ecology in the Mediterranean remains poorly understood.

The non-consumptive use of sea turtles has become a rapidly growing sector of the global tourism industry and is increasingly recognised as an important source of economic benefit for coastal communities. In the Maldives, however, the socio-economic value of sea turtles remains poorly quantified. Building on a preliminary survey conducted in 2019, this study provides a comprehensive assessment of the socio-economic value of sea turtles to the tourism industry, post-pandemic, while identifying sea turtle viewing hotspots with high tourism pressure that may require stricter regulation. Questionnaires collected information on operations related to sea turtle excursions in 2022, including the estimated direct spend on sea turtle excursions and the perceived value of sea turtles to tourists and operators. Results include responses from 117 tour operators across 20 atolls in the Maldives, with 68% from resort operators, 27% from local island operators, and 5% from liveaboards. Maldivian nationals made up 55% of respondents and 78.8% of the people working, directly or indirectly, on sea turtle excursions in 2022. The direct revenue generated by sea turtle tourism in the Maldives is estimated at US$10.9-14.4 million in 2022, with individual turtles at high-use sites generating up to US$29,709 per year. These findings underscore the significant economic and social importance of sea turtles to the tourism industry in the Maldives, matching that of manta rays and sharks, and highlights the need for improved conservation efforts to safeguard local sea turtle populations and their associated benefits for Maldivian communities.

Benthic communities form the foundation of food webs in coastal and shelf seas worldwide. However, these communities face severe threats from anthropogenic bottom-disturbing activities. Marine Protected Areas (MPAs) effectively safeguard benthic communities against such disturbances. Nevertheless, the effectiveness of MPAs for the recovery of benthic communities in highly dynamic soft-bottom areas is much debated, as these communities are thought to be adapted to natural dynamics and therefore resistant to human impacts. In this study, we examine whether MPAs in highly dynamic seas support sensitive communities that are affected by bottom-disturbing fishing gear. Utilising a Before-After-Control-Impact (BACI) experimental design, we investigated the effects of disturbance caused by a shrimp trawl gear on macrozoobenthic communities within MPAs in a dynamic coastal soft-bottom sea over two years. We assessed changes in taxonomic and functional diversity, as well as community composition, across three levels of trawling intensity and frequency (low intensity and high frequency, high intensity and low frequency, and high intensity and high frequency) compared with undisturbed control areas. The study was carried out in the lower dynamic areas of the study system, where we found that, even light trawling gear impacted functional diversity and community assembly of macrozoobenthic communities, leading to shifts in functional groups. Contrastingly, taxonomic diversity metrics were not affected. We found that taxonomic and functional turnover increased stronger over time than the undisturbed control, with the highest turnover in the most frequently disturbed treatments. Long-living species were negatively impacted by disturbance, and the abundance of scavengers and predators increased in trawled areas, with possible radiating effects into undisturbed areas, while suspension feeders declined. Our findings demonstrate that anthropogenic disturbance remains a relevant ecological pressure, even in areas that may appear resilient due to their dynamic nature. MPAs can then provide ecological benefits by protecting sensitive and functionally important species. Article Impact StatementMarine Protected Areas are effective in safeguarding sensitive communities from anthropogenic disturbance.

The increasing impact of humans on natural habitats leads to an increase in human-wildlife conflict (HWC), specifically when there is competition for shared resources. In freshwater systems such as Lake Nasser, Egypt, co-occurrence of local fishermen communities with Nile crocodiles (Crocodylus niloticus) poses critical challenges for both livelihoods and biodiversity conservation. Understanding local perception of crocodiles by local fishermen is therefore essential for developing effective and socially accepted management responses. We used a structured questionnaire to assess how fishermen perceive and respond to crocodiles across three attitudinal domains: (1) perceived threats, (2) perceived economic benefits, and (3) conservation or co-existence values. Forty-two fishermen were interviewed across multiple khors (side arms of the lake). The responses showed a multifaceted picture: while many local fishermen associated crocodiles with gear damage, reduced catches, and livelihood risks, support for crocodile protection and recognition of their ecological role were also widespread. Interest in crocodile-based livelihood opportunities, such as harvesting or collecting the hatchlings, was generally low, suggesting social, cultural, or legal barriers to such approaches. Fishing experience influenced perceptions, with fishermen encountering crocodiles more frequently reporting decreased catches and greater concern. Cluster analysis further revealed three different respondent groups with different attitudes: conflict-oriented, moderate, and coexistence-oriented. Support for crocodile protection was the strongest predictor of belonging to the pro-co-existence group. Our findings underscore the complexity of human- crocodile co-occurrence in Lake Nasser and, on a wider scale, add to the existing cautions against simplistic mitigations of local HWC. Effective conservation and livelihood interventions will require participatory, context-sensitive approaches that integrate the different perceptions and attitudes of local people.

The queen conch (Aliger gigas) is a key native species of the Caribbean Sea and a primary source of income for thousands of fishers. Historically, it has been a highly valuable resource for the fishing sectors of countries such as the Bahamas, Turks and Caicos, Honduras, and Nicaragua. However, due to its high economic value, the species has been extensively overfished across the region. Overfishing, combined with limited larval dispersal, low recruitment, and poor population connectivity, has led to a drastic decline in population numbers of the species, resulting in its current classification as Threatened. Despite this status, likely impacts of climate change on its populations remain poorly understood, posing significant challenges to conservation efforts. To address this gap, we integrated occurrence records, climate data, and satellite-derived marine habitat data to develop ecological niche models estimating the current and future distribution of the queen conch under different climate change scenarios. We found substantial losses of suitable areas for queen conch along the northern Atlantic coast of South America and Central America, part of the Greater Antilles and the Lesser Antilles. The entire Caribbean region is projected to lose suitability entirely within 20-30 years under the moderate and most extreme climate scenarios. Conversely, our models estimate some suitable areas to persist or expand along the southeastern coast of the United States at least until sometime between 2040 and 2060. Overall, our results suggest a northward shift in the range of this species, with the magnitude of this shift closely tied to the severity of climate change impacts. This work aims to build upon and enhance existing knowledge about survival of queen conch populations in the Caribbean over time. Anticipating future habitat availability will be key to protecting this economically and ecologically important species.

The use of marine space by human activities is globally increasing, resulting in a competition with spatial management measures for marine conservation. Within the European Union (EU) these measures are currently implemented by the union member states to achieve the UN sustainable development goal (SDG) of protecting at least 10 % of the national marine waters. Further, the EU Marine Strategy Framework Directive (MSFD) and the Nature Restoration Regulation (NRL) are the two main legal means for the implementation of ambitious spatial conservation targets for benthic habitat types, which can range from 10 - 90 %. This study analysis how the targets of the MSFD and NRL are currently met in the German waters of the North Sea and which areas the full implementation of both legislations might require. A spatial optimisation tool ("prioritizr" in R) was used to identify optimised solutions for the conservation of up to 75 % of NRL benthic habitats. The current spatial conservation measures (which ban demersal trawling within certain zones of designated marine protected areas, MPA) are not sufficient to reach the targets of the MSFD and NRL. Extending the exclusion of demersal trawling to the entire area of the MPAs would achieve a sufficient coverage for all habitats except for offshore sand and mud habitats. These could be further protected, when including areas for offshore wind farms, where trawling is also banned. However, to date it is unclear, if and how these (or other human use) areas could be included into spatial conservation regimes, a debate that needs to be resolved to allow for the achievement of the ambitious MSFD and NRL targets.

The non-indigenous brown macroalga Rugulopteryx okamurae has emerged as one of the most aggressive marine invaders in European waters, deeply altering benthic communities and causing severe socioeconomic impacts. While its expansion has been extensively documented along the southern Iberian Peninsula, understanding the dynamics of its northward range expansion along the Spanish Mediterranean coast remains critical for coastal management. This study documents the first formal record of R. okamurae in Calpe (Alicante), representing its current northernmost distribution limit within the Comunitat Valenciana. Sampling was conducted through an initial opportunistic scuba diving observation along the surrounding waters of the Penyal dIfac Natural Park, followed by targeted underwater surveys and an ad hoc inspection of commercial bottom-trawling nets drying at the port of Calpe during June 2026. Morphological and anatomical identification was confirmed through cross-sections of the thallus under optical microscopy, revealing the presence of both the thick and intermediate morphotypes of the species. The collected specimens were found either entangled within a native photophilic algal canopy in shallow waters or recovered from deeper offshore fishing grounds. Given the absence of records in the area during 2023-2025 surveys, these findings suggest either a very recent front-wave colonization event or a contribution from nearby, yet undetected, established patches, driven by secondary local dispersal mechanisms such as drifting fragments and explicitly highlighting commercial fishing activities as an active vector. Furthermore, considering that the species was recorded within a marine protected area and deeper environments, these results highlight a potential ecological threat to local benthic ecosystems, emphasizing the urgent need f or competent authorities to implement spatiotemporal monitoring and public awareness campaigns to prevent the definitive establishment of this invader.

BACKGROUNDOceanic islands and seamounts are recognised as hotspots of abundance and diversity for marine top predators, such as sharks and large teleosts, and are hypothesised to function as migratory stepping stones for mobile, pelagic species. However, while movements of pelagic predators between such features have been documented in some oceans, evidence from the tropical Atlantic remains limited. RESULTSHere, we report on long-distance migrations of three species of pelagic predator between oceanic islands and seamounts in the tropical south Atlantic recorded via independent passive acoustic telemetry arrays. These include the first recorded trans-Atlantic migration of a Galapagos shark (Carcharhinus galapagensis) from Ascension Island (UK) to the Sao Pedro and Sao Paul Archipelago (Brazil) (minimum distance 1,930 km); the longest documented oceanic migration of an Almaco jack (Seriola rivoliana) from St Helena (UK) to Ascension Island (minimum 1,300 km); and multiple movements of Galapagos and silky sharks (C. falciformis) between two Mid-Atlantic Ridge seamounts and Ascension Island (minimum 265-325 km). These detections are notable given the limited duration, sample sizes, and temporal overlap of acoustic tracking studies in the region, suggesting substantial connectivity across large spatial scales. CONCLUSIONSOur findings provide empirical support for the role of oceanic islands and seamounts as connectivity hubs for pelagic predators in the tropical Atlantic, underscoring their importance as key nodes in marine protected area networks. More broadly, this study demonstrates the value of collaborative regional tracking networks in resolving large-scale movement patterns and informing marine management at ecologically relevant scales.

Designing effective spatial management for chondrichthyans (sharks, skates, rays and chimaeras) requires incorporating critical areas, sites essential for population maintenance, such as reproductive and feeding areas. Yet most area-based measures have been developed without consideration of chondrichthyan habitat use. The Important Shark and Ray Area (ISRA) initiative has been pivotal in designating priority areas through a rigorous, consultative process. To complement this, our study offers researchers a testable definition for generating robust evidence to strengthen future critical area delineations and related management decisions. We define critical areas using three criteria: 1) relative frequency of use, (2) extended within-year occupancy and (3) repeated use across years. This framework enables objective comparison among candidate sites and is generalisable across different critical area types. The definition builds upon established early-life-stage habitat concepts and applies these to broader life-history functions. The utility of this framework is then demonstrated through a systematic review of contemporary peer-reviewed literature of critical chondrichthyan areas in the European Atlantic. The review highlighted 62 critical areas with Strong evidence and 41 areas of Moderate strength evidence, which informed the European Atlantic ISRA selection process. Research effort was concentrated in inshore areas, particularly around the British Isles and Portugal, with biases towards large, threatened and commercially valuable species, whilst chimaeras were notably underrepresented. Early-life stage areas were most frequently identified, whereas resting areas were rarely documented. Evidence patterns and biases are examined in the context of evolving critical area concepts to advance their development and improve the quality and breadth of future research. By outlining a testable definition, identifying key knowledge gaps, and proposing research and reporting guidelines, this work enhances the consistency, comparability, and spatial coverage of future chondrichthyan habitat research to support its application to conservation planning.

Philippine freshwater ecosystems are considered one of the most diverse ecosystems harboring numerous fish species. However, in the Philippines, these ecosystems are threatened by invasive species that potentially disrupt ecological balance. In this study, we focused on the vermiculated sailfin catfish Pterygoplichthys disjunctivus, an invasive aquarium species reported in several Philippine aquatic ecosystems. Despite its documented spread, its potential range under a rapidly changing climate remains poorly understood for the country. Hence, in this study, we utilized the MaxEnt model to predict its near-current and future habitat suitability in the Philippines. Using 11 reported occurrences, our model showed high predictive accuracy (AUC = 0.882{+/-} .034, TSS = 0.7394 {+/-} 0.154, SEDI = 0.971 {+/-} 0.019). Across the current and future scenarios, slope was the primary contributor (78.7% - 81.3%), followed by BIO 10 or the mean temperature of the warmest quarter(18% - 27.8%), and flow accumulation (0% - 5.2%). However, for the SSP126 scenario, BIO10 is projected to triple by 2050 (18 - 48%). Current projections identify high-risk regions, particularly central Luzon (Laguna de Bay and Lake Taal), the Cagayan River Valley, and portions of eastern Mindanao (Agusan Marsh and Lake Mainit). Sankey transition analysis confirms a high habitat stability rate (>73%) for high-suitability pixels in both SSPs, indicating persistent invasion risk. Overall, our study provides a framework for invasive species management and contributes to the conservation of Philippine aquatic ecosystems.

Sakumo Lagoon, a small (1 km2) semi-open coastal lagoon in Ghana, lies between the cities of Accra and Tema. The lagoon and its surrounding wetland were designated a Ramsar Site in 1992, mainly because it served as a refuge for 66 local and migratory bird species. Its ecology, and the biology of its major fish species, notably the blackchin tilapia (Sarotherodon melanotheron) were thoroughly studied in 1971, when the lagoon was a diverse, mainly brackish ecosystem supporting a traditionally and well-managed fishery. In 2016-2017, another study found the lagoon mostly covered by floating vegetation and plastic waste. Finally, in 2024, a visual survey established that the floating vegetation had been almost completely replaced by terrestrial plants, with only a few square meters of garbage-strewn water in front of a culvert connecting the lagoon to the open sea. Several lagoons along the coast of Ghana have been similarly lost to urban sprawl and its various forms of pollution, but Sakumo Lagoon is a Ramsar Site, and its imminent disappearance should not remain undocumented.

The rariphotic zone, typically spanning depths of approximately 130 to 300 meters, represents a key transition between light-dependent coral reef ecosystems and the aphotic deep sea. Despite its potential ecological importance, including its proposed role as a refuge for species exposed to climate-driven stress, rariphotic ecosystems remain poorly understood. In this study, we conducted a systematic review and synthesis of the scientific literature on these habitats from 1970 to 2025. Following the PRISMA 2020 protocol, we analyzed 185 studies to characterize the historical development of research, identify geographic and methodological biases, and assess shifts in research priorities over five decades.Our results show a marked increase in research effort over the last decade, driven in part by advances in underwater technologies such as Remotely Operated Vehicles (ROVs), Human Occupied Vehicles (HOVs), and Baited Remote Underwater Video Station (BRUVS). However, this growth remains uneven, with persistent biases toward benthic rather than pelagic studies and a strong concentration of research in geographically accessible regions. Multivariate analyses of research novelty indicate that technological innovation and the formal recognition of the rariphotic zone in 2018 corresponded with major structural shifts in literature. Although the rariphotic zone is now increasingly recognized as an ecologically distinct component of the reef continuum, it remains underrepresented in ecological theory and conservation frameworks. Future research should move beyond descriptive taxonomic mapping toward integrative, data-driven functional ecology, with particular emphasis on long-term monitoring and depth-stratified connectivity.

Downstream migration and sea entry are periods of high mortality for sea trout smolts and migration timing is a critical aspect of survival. We aimed to investigate migration timing of PIT-tagged sea trout smolts across a latitudinal gradient in five freshwater systems across Europe: Norway, Sweden, Denmark, France and Portugal. In two systems, smolt migration was further examined to assess a) differences in sex, body size and condition between autumn and spring migrants; b) the influence of spatial origin within the stream; and c) relationships between individual body size and migration date. Tagged smolts were not detected migrating in the Portuguese watershed. Spring migration timing differed significantly between watersheds in Norway, Sweden, Denmark and France. Generally, there was a trend of earlier migration at lower latitudes. Autumn vs spring migration was examined in Gudso-Denmark. Autumn migrants were larger in both length and mass, with no differences in sex ratios or body condition. Fish originating from an upstream site were more likely to migrate in the autumn compared to the spring and vice versa. Size dependent migration was found in the Swedish system, Haga [a]-Sweden, with larger individuals migrating earlier in the spring than smaller individuals. Outward-migrating smolts were also more likely to originate from a downstream site than an upstream site. Overall, these results show both large-scale geographic and fine-scale individual influences on migration timing. Given that climate change may have large impacts on migration patterns in sea trout, understanding variability in migratory patterns across a latitudinal gradient is an important tool for predicting responses to environmental changes.

Octocoral colonies with unusual morphology were detected in September 2022 and October 2023 in two coastal areas east of Havana, Cuba, and tentatively identified as Unomia stolonifera. U. stolonifera is an invasive octocoral from the Indo-Pacific that was first reported in the Caribbean off Venezuela in the 2000s, where it has spread rapidly, smothering coral reefs and substantially altering benthic communities. After obtaining tissue samples from a Cuban octocoral colony, we re-examined the specimen using molecular barcoding of three mitochondrial regions (16S/ND2, mtMutS, COI) and the nuclear large ribosomal subunit (28S rRNA), and we unequivocally identified it as Xenia umbellata. X. umbellata, a native of the Red Sea, was first identified in southern Puerto Rico in October 2023 and has since been found in various marine ecosystems along the southern coast of the island. The presence of either invasive octocoral species in Cuba or elsewhere in the Caribbean would be of a serious environmental concern due to their documented tolerance, totipotentiality, propagation capacity and significant negative interactions with local benthic fauna. Attempts to eradicate the invasive soft coral colonies from Cuban waters have been initiated with apparent success, helping to control further expansion. The most likely introduction pathway is the accidental or intentional releases from the aquarium trade but transport via ballast water cannot be ruled out. We cannot discount the possibility of independent invasion events from different routes to Puerto Rico and Cuba occurring within a year of each other. Propagation from Cuba to Puerto Rico, or vice versa, which we consider highly improbable, would likely imply that soft coral populations may also have been established on Hispaniola but have remained undetected in the Dominican Republic and Haiti to date.

Habitat degradation and biodiversity loss in the Black and Azov Seas necessitate improved tools for spatially explicit conservation planning. We employed stacked species distribution modelling (SSDM) to assess habitat quality for the three resident cetacean species, the common dolphin (Delphinus delphis ponticus), the bottlenose dolphin (Tursiops truncatus ponticus), and the harbour porpoise (Phocoena phocoena relicta), which serve as apex predators and indicators of ecosystem health. Occurrence data were compiled from the Global Biodiversity Information Facility (GBIF), and ensemble species distribution models (ESDMs) were constructed using nine algorithms within the SSDM framework, with eight environmental predictors extracted from Bio-ORACLE v3.0. Individual ESDMs demonstrated excellent predictive performance (AUC: from 0.82 to 0.83; TSS: from 0.65 to 0.67; prop.correct: from 0.82 to 0.83). However, the initial continuous stacking method (pSSDM) yielded low community-level prediction success (0.36), prompting evaluation of three correction approaches. The Probability Ranking Rule (PRR) substantially improved performance (prediction.success = 0.459, sensitivity = 0.704, Jaccard = 0.465), effectively mitigating the overprediction bias inherent in stacked models. Species richness mapping identified multi-species hotspots along the southwestern Black Sea shelf, the Crimean coast, the Kerch Strait, and parts of the eastern coast, while the deep central basin exhibited the lowest richness. Variable importance ranking revealed bathymetry as the primary community-level driver (41.2%), followed by dissolved oxygen (13.8%), sea surface temperature (11.9%), and salinity (10.4%). Species-specific importance patterns confirmed ecological niche segregation, with common dolphins favouring deeper offshore waters and bottlenose dolphins and harbour porpoises associated with shallower shelf environments. The moderate richness observed in the highly productive northwestern shelf, despite high nutrient inputs, may reflect a combination of natural factors (elevated turbidity, reduced salinity) and anthropogenic pressures (fisheries bycatch, shipping, coastal development, and military activity) that limit species co-occurrence. Our findings demonstrate that PRR-corrected SSDM provides a robust framework for mapping cetacean habitat quality and identifying conservation priorities in the Black and Azov Seas, offering an evidence-based tool to inform ecosystem-based management in this ecologically unique and increasingly pressured marine region.

The biodiversity crisis is exacerbated by persistent gaps in taxonomic, geographic, and conservation knowledge. This study provides a comprehensive assessment of Linnean, Wallacean, and conservation shortfalls in Rivulidae (Cyprinodontiformes), one of the most diverse families of Neotropical freshwater fishes. To this end, an extensive dataset was compiled, comprising 494 valid species, 51 synonyms, 3,419 occurrence records, and information on life cycle, distribution, and conservation status. The Linnean shortfall remains open: after 1975, the rate of species description increased sharply, and estimates indicate that 103 species remain undescribed (95% CI: 53-212). The year of species description was influenced by detectability and accessibility factors, with larger species, more widely distributed species, and species occurring in more densely populated areas being described earlier. The Wallacean shortfall was broad and spatially uneven: only 5.34% of the region was considered adequately sampled. The conservation shortfall was also substantial: 179 species are threatened with extinction, 69 species remain Not Evaluated, and 62 are Data Deficient. The mean time between taxonomic description and first IUCN extinction-risk assessment was 25.7 years. Moreover, 59.9% of species have no records within protected areas, including 69.3% of threatened species. These findings synthesize an urgent challenge: biodiversity knowledge and conservation shortfalls must be overcome simultaneously to protect species that are still being discovered, remain poorly documented spatially, and are restricted to habitats under intense anthropogenic pressure. The conservation of Rivulidae cannot wait for complete knowledge; action amid uncertainty is necessary to prevent both known and unknown species from disappearing.

Early detection and monitoring of non-indigenous species (NIS) is crucial to prevent their establishment and to reduce ecological and economic impacts in coastal ecosystems. Traditional monitoring approaches, which rely largely on morphological identification of collected organisms, are often time-consuming and may fail to detect species that occur at low abundance, are morphologically cryptic, or are present in the form of inconspicuous life stages. DNA-based approaches, particularly those resorting to environmental DNA, have demonstrated high aptitude for biodiversity monitoring and biosecurity surveillance. By examining the genetic material from bulk community samples or released into the environment, DNA-based approaches enable the detection of species without the need for direct observation, thereby increasing detection sensitivity and expanding the scope of monitoring programs. Despite the rapid growth of its employment in marine monitoring, a global synthesis of the status and trends of DNA-based approaches for detecting NIS in this environment has been lacking. Here, we present such synthesis, based on 146 published studies employing DNA for NIS detections in coastal environments. Two main methodological approaches were used across the reviewed studies, namely DNA metabarcoding which was applied in 49% of studies, closely followed by targeted single-species PCR assays, used in 42% of the studies. A smaller proportion of studies (10%) combined both approaches, integrating broad community screening with targeted detection to improve surveillance efficiency. Globally, 752 NIS were detected across disparate taxonomic groups, with metazoans representing the largest proportion of detections (464 species), followed by Chromista (210 species) and Plantae (77 species). Among these, the most frequently detected taxonomic groups included Dinophyceae (Dinoflagellata), Teleostei (Chordata), Florideophyceae (Rodophyta), Polychaeta (Annelida), Copepoda and Malacostraca (Arthropoda), and Ascidiacea (Chordata). At the species level, several well-known marine invaders were recurrently reported, including Bugula neritina (Linnaeus, 1758), Styela plicata (Lesueur, 1823), Acartia (Acanthacartia) tonsa Dana, 1849-1852, and Botryllus schlosseri (Pallas, 1766), highlighting the ability of DNA approaches to detect widespread and established invaders across different regions. The mitochondrial cytochrome c oxidase subunit I (COI) gene was the most widely used genetic marker, reflecting its broad taxonomic coverage and extensive representation in reference databases, particularly for targeting Metazoa. Ribosomal RNA genes, particularly 18S and 16S rRNA gene markers, were also frequently employed to target a wider range of eukaryotic taxa. Regarding sampled substrates, water was by far the most analyzed substrate, followed by zooplankton and biofouling communities collected from man-made structures. Notably, approximately 31% of all NIS detections reported in the reviewed studies constituted new regional records. These results highlight the potential of eDNA for coastal monitoring but also underline important limitations. Persistent geographical, taxonomic, and methodological biases can affect detection outcomes, and reliance on single sample types or markers may increase false negatives - particularly critical for NIS early detection. Therefore, multi-marker and multi-substrate approaches are essential to improve detection reliability and support effective biosecurity strategies. As reference databases continue to expand and methodological protocols become increasingly standardized, DNA-based monitoring is likely to play a central role in future management and surveillance of biological invasions in coastal ecosystems. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=133 SRC="FIGDIR/small/722998v1_ufig1.gif" ALT="Figure 1"> View larger version (75K): org.highwire.dtl.DTLVardef@17948b1org.highwire.dtl.DTLVardef@193832dorg.highwire.dtl.DTLVardef@189033dorg.highwire.dtl.DTLVardef@33cddf_HPS_FORMAT_FIGEXP M_FIG C_FIG

Littoral mysids facilitate benthic-pelagic coupling through horizontal migration, yet quantitative monitoring in structurally complex habitats remains methodologically challenged where traditional active gears fail. We evaluated the efficacy of standardized light traps for monitoring littoral mysids (Neomysis integer, Praunus flexuosus) and mesopredatory three-spined sticklebacks (Gasterosteus aculeatus) in the northern Baltic proper, Baltic Sea. Using a paired experimental design with predator-exclusion and unmodified traps, alongside concurrent passive benthic trapping, we assessed abiotic drivers affecting catchability, biotic interactions, and statistical power to monitor changes in population size over time. Results indicated significant biotic interference: unmodified traps attracted high densities of sticklebacks, which reduced mysid catches by approximately 85% through predation or behavioural avoidance. Consequently, physical predator exclusion is mandatory for accurate mysid sampling. Generalized Linear Mixed Models (GLMMs) confirmed that catch rates for all taxa were primarily driven by night duration rather than water temperature. While passive benthic trap catches tracked metabolic activity (peaking in warm summer months), light trap efficiency peaked in spring and collapsed during summer, confirming that sampling efficiency was strictly limited by the short duration of the night. Simulation-based power analysis revealed a stark contrast in monitoring utility based on spatial aggregation. For highly aggregated mysids, the method demonstrated low precision (Power < 0.25 to detect a 50% decline), rendering it suitable primarily for detecting substantial population collapses (>90%). In contrast, for less aggregated sticklebacks, the method achieved a more robust statistical power (>0.80 for a 60% decline), validating light traps as a precise tool for monitoring these abundant mesopredators. We conclude that light traps fill a critical methodological gap for winter and early spring monitoring when traditional passive gears underperform. Appropriate abundance indices should be based on statistical models accounting for night duration and strictly employ physical exclusion barriers when targeting mysids.

1.We conducted field surveys over two consecutive years (2022 and 2023) of freshwater habitats in the Rio De La Concepcion (several tributaries and sites) and one site in the Rio Santa Cruz (tributary of the Gila River) in the state of Sonora, Mexico. Our primary goal was to detect the presence of the Rio Concepcion Topminnow (Poeciliopsis jackschultzi), an endangered microendemic livebearing desert fish whose external morphology is indistinguishable from several sympatric congeners. Using an environmental DNA (eDNA) metabarcoding approach ("MiFish" locus), we failed to detect evidence of P. jackschultzi, implying that it is extinct or present at abundances below our detection ability. Applying a collective evidence approach including visual/eDNA surveys and past records, we discuss the strengths and limitations of the eDNA metabarcoding approach. In the Rio De La Concepcion, we confirm the presence of the other known native and previously reported introduced teleosts, and reveal more recent introductions. In the Rio Santa Cruz site, we detect three putative non-natives (Asexual Hybrid Topminnow, Yaqui Sucker, and Mexican Roundtail Chub). We recommend further monitoring of habitats and fish taxa, and implementation of practices that improve groundwater recharge and the quality and quantity of treated wastewater in the study area.